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	<h1 id="firstHeading" class="firstHeading" lang="en">Hugin Exposure tab</h1>
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		<div id="mw-content-text" lang="en" dir="ltr" class="mw-content-ltr"><div class="mw-parser-output"><p>As explained on the <a href="Hugin_Photos_tab.html#Photometric_.28Simple_User_interface.29" title="Hugin Photos tab">Hugin Photos tab</a>, hugin has a brightness and colour correction system using the default nona stitching tool.
</p><p>Hugin comes with an extended set of predefined settings for photometric optimisation. If these predefined options do not give the desired results you can define your custom parameters in this <b>Hugin Exposure tab</b>.
</p><p>The images list behaves very similar like the image list on the <a href="Hugin_Photos_tab.html" title="Hugin Photos tab">Photos tab</a>. So can also in this tab add/remove images, change the lens or stack assignments, link or unlink image variables,... Beside the features of the list on the <a href="Hugin_Photos_tab.html" title="Hugin Photos tab">Photos tab</a> it provides also in-place editing of single image variables. (<b>Note:</b> If you want to modify a value for a lens, you need to single-click the value, not double-click it.) If you want to change image variables from several images at once, select all affected images and choice <b>Edit image variables...</b> from the context menu.
</p>
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<h1><a name="Photometric_Optimisation"><span class="mw-headline">Photometric Optimisation</span></a></h1>
<p>With Ctrl+Left click you define which parameters will be optimised. The context menu provides short cuts to select the parameters of all images, of all images of a selected lens or of all image of a single stack.
</p>
<h2><a name="Image_variables"><span class="mw-headline">Image variables</span></a></h2>
<p>In the <b>Image variables</b> part of the screen you can modify the exposure EV, the <i>red multiplier</i> <b>Er</b> and the <i>blue multiplier</i> <b>Eb</b>.
</p><p>The <b>Red multiplier</b> and <b>Blue multiplier</b> settings are used to account for changes
in <b>white balance</b> (also known as <i>colour balance</i> or <i>colour temperature</i>) between
photos.  Setting them both to <i>1</i> will result in no <i>white balance</i> change (the numbers
are relative to the green channel which stays unaltered).
</p><p>As with exposure, different photos in the same project are quite likely to require different
<i>white balance</i>.  Typically this will be caused by variations in lighting conditions between
shots - For example a cloudy scene will contain considerably less <i>red</i> light than the same scene
under direct sunlight.
</p>
<h2><a name="Camera_and_Lens_variables"><span class="mw-headline">Camera and Lens variables</span></a></h2>
<p>The values that you can change in the <b>Camera and Lens variables</b> table is again dependent on the <b>Simple</b>, <b>Advanced</b> or <b>Expert</b> User interface.
</p>
<h3><a name="Vignetting"><span class="mw-headline">Vignetting</span></a></h3>
<p><a href="Vignetting.html" title="Vignetting">Vignetting</a> is dependent mainly on your lens and the <i>aperture</i>. Usually the
centre of the image is brighter with a falloff towards the edges.  The three
numbers here represent a polynomial curve used by <a href="Hugin.html" title="Hugin">hugin</a> to correct vignetting.
</p><p>You are not expected to guess these values, they are generally loaded with a lens
profile or calculated from two or more overlapping photos.
</p><p>Set the values to <i>0,0,0</i> for no vignetting correction.
</p><p>Usually all photos taken with the same <i>lens</i> will have the same vignetting, keep
<b>Link</b> checked to ensure <b>hugin</b> applies the same vignetting correction to all
photos with the selected lens number.
</p>
<h3><a name="Vignetting_Center_Shift"><span class="mw-headline">Vignetting Center Shift</span></a></h3>
<p>The centre of <a href="Vignetting.html" title="Vignetting">vignetting</a> is rarely the exact centre of the photo. The two numbers
here indicate the position of the vignetting centre. The scale is in pixels, with
<i>0,0</i> indicating the centre of the photo. The values are independent of the <b>d</b>
&amp; <b>e</b> parameters which specify the origin for projection and geometric distortion.
</p><p><br />
</p>
<h3><a name="Camera_Response"><span class="mw-headline">Camera Response</span></a></h3>
<p>The <a href="Camera_response_curve.html" title="Camera response curve">camera response curve</a> is used both for mapping the images to a linear
colourspace when creating <a href="HDR.html" title="HDR">HDR</a> output, and for normalising the colourspace
for internal vignetting, brightness and colour corrections when creating
'normal' <b>LDR</b> output.
</p><p><a href="Hugin.html" title="Hugin">hugin</a> uses the <a rel="nofollow" class="external text" href="http://www1.cs.columbia.edu/CAVE/projects/rad_cal/rad_cal.php">EMoR response model</a>
from the Computer Vision Lab at Columbia University which simplifies the full
response curve to these five empirical coefficient numbers.  You are
not expected to guess these values, they are generally loaded with a lens
profile or calculated from two or more overlapping photos.
</p><p>Set the five numbers to <i>0,0,0,0,0</i> to use a generic response curve or change the <b>Type</b>
to <b>Linear</b> to indicate that your input photos have a <i>scene-referred</i> or <a href="HDR.html" title="HDR">HDR</a>
response.
</p><p>Keep <b>Link</b> checked to ensure <b>hugin</b> applies the same
response curve to all photos with the selected lens number.
</p>

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